Stealth File Share

The Stealth File Share module allows users to send and receive encrypted files through a fully decentralized and privacy-preserving system. Files are encrypted locally inside the browser using Lit Protocol before being uploaded to Lighthouse (IPFS-based decentralized storage). No central server, gateway, or API proxy ever sees the plaintext content or keys.

How It Works

1. Client-Side Encryption (Lit Protocol)

   • When a user selects a file, Crosterix uses Lit Protocol’s encryptFile() method to symmetrically encrypt it.

   • The symmetric encryption key is then encrypted with the recipient’s wallet public key and stored on the Lit network.

   • Only the wallet that owns the corresponding private key can decrypt and retrieve the file.

   import * as Lit from "@lit-protocol/sdk-nodejs";
   
   const { encryptedFile, encryptedSymmetricKey } =
     await Lit.encryptFile(file, recipientPubKey);

2. Decentralized Storage (Lighthouse / IPFS)

   • The encrypted file (.lit) is uploaded to Lighthouse, an IPFS-based decentralized storage network with retrieval and gateway APIs.

   • Lighthouse provides a CID (Content Identifier) for the uploaded file.

   • Crosterix never stores this CID centrally; it’s only referenced locally and optionally recorded in Supabase for expiration tracking.

   const response = await lighthouse.upload(encryptedFile, userApiKey);
   const cid = response.data.Hash;

3. Expiration & Metadata (Supabase)

   • Crosterix uses Supabase as a lightweight metadata database to track:

     • File CID

     • Encryption key hash

     • Expiration time (e.g., 24 hours or 1 access)

     • Access count

   INSERT INTO file_links (cid, key_hash, expires_at, max_access)
   VALUES ('bafkre...', '0xabc...', NOW() + INTERVAL '24 hours', 1);

   • Once the expiration time or access count is reached, the link automatically becomes invalid.

4. Access Control

   • When the recipient opens the link, the DApp verifies that their wallet can derive the decryption key from Lit Protocol.

   • If verified, Crosterix decrypts the file locally in the browser — no backend interaction occurs.

   • Unauthorized wallets cannot decrypt or access the data even if they possess the CID.

Security Properties

Layer	Mechanism	Benefit
Encryption	AES-GCM + asymmetric key wrapping (Lit)	End-to-end confidentiality
Storage	IPFS via Lighthouse	Decentralized persistence
Access	Wallet-based key derivation	Only authorized wallets can open
Metadata	Supabase (TTL & counter)	Auto-expire links
Execution	100% client-side	No data leakage to servers

Developer Integration Example

import { uploadEncryptedFile } from "@crosterix/sdk";

const link = await uploadEncryptedFile({
  file,
  recipient: "0xRecipientAddress",
  expiresIn: 86400, // seconds
  maxAccess: 1,
});

console.log("Private link:", link);

This generates a stealth download link such as: https://app.crosterix.io/share/bafkre...#accessKey=0x...

Only the wallet with the correct decryption key can open the file.